1. Field of the Invention
This invention relates to a community office (C.O.) switching system in which the uppermost element of its common control hierarchy is a stored program processor. More particularly, it relates to the portions of such a system which are involved in the function of sensing or transmitting supervisory events.
2. Description of the Prior Art
In known prior art C.O. switching systems, the uppermost element of the common control hierarchy have been stored program processors which operate in an interrupt mode.
Following is an example of what is meant by the interrupt mode in sensing or transmitting 100 millisecond wink or 100 millisecond hookflash supervisory events, the processor responds to 10 consecutive interrupts from a 10 millisecond clock. For each of these responses, the processor must test the state of the supervision signal. Such operation is an interrupt mode results in a number of limitations and disadvantages as follows:
a. The processor spends considerable of its time in the overhead function of servicing the interrupts.
b. The stored program is complex and requires considerable memory space, and in turn dictates that the stored program processor be of large enough capacity to handle the more complex larger programs. This is particularly true where the stored program is designed for modularity.
c. C.O. switching systems must be monitored for automatic fault detection. A stored program processor operating in the interrupt mode is quite difficult to monitor for automatic fault detection.
One prior art approach to lessening the effect of these limitations and disadvantages has been to employ a second processor as an automatic scan advice for detecting seizures and abandonments of seizures. However, this approach merely allows the uppermost (in hierarchy) processor to operate with a reduced number of interrupts.
The other mode of operation of a stored program processor is called the "polling mode" in which the processor polls the status of an external device (such as a queueing register) to receive its next processing task. The foregoing limitations and disadvantages are not present in the case of a processor employed in a polling mode. The polling mode can be used only if the processing load presented to the processor (particularly the maximum rate at which processing tasks are received) can be "worked off" by the processor in time to obtain results within the "real time" constraints of the system.
Heretofore, there has been no known case of a C.O. switching system in which the upper most element of the common control is a stored program processor which totally operates in the polling mode. The frequency with which processing tasks present themselves to the processor depends upon both the number of lines and trunks of the switching system, and the busy hour call rate through the switching system. Prior to the present invention, the quantity of lines and trunks and the busy hour call rate capacity which are normal by commercial standards, have presented processing loads which have required the use of the interrupt mode.
Accordingly, among the objects of the invention are:
1. To provide a stored program processor common control for a C.O. switching system which has a system architecture enabling the stored program processor to be used more efficiently than has heretofore been possible with prior art systems.
2. To provide a stored program processor common control for a C.O. switching system which has a system architecture enabling use of a smaller capacity stored program processor than has heretofore been possible with prior art systems.
3. To provide a C.O. switching system in which the uppermost element of its common control hierarchy is a stored program processor which operates in a polling mode.
4. To provide a switching system as stated in objective 3, which efficiently processes calls for a system having quantities of lines and trunks and having a busy hour call rate capability in accordance with commercial norms.